Certain agricultural soils, especially in the south, have grown crops almost continuously for more than 100 years. Such soils are now very low in organic matter content and are therefore generally infested with soil borne plant pathogenic fungi represented by the fungal species Rhizoctonia, Pythium and Fusarium among others (Crawford, J. L. 1975. Plant Disease Reporter, 56:373). Such soils are said to be "conducive" to plant disease causing agents. Our experience teaches that such soils low in organic matter remain conductive to plant disease causing agents unless they are amended with a high nitrogen to carbon ratio plant compost material as disclosed in U.S. Pat. Nos. 4,164,405 and 4,229,442, issued to Pinckard, Aug. 14, 1979 and Oct. 21, 1980, respectively. Soils that have been cleansed of plant disease causing agents are said to be made "suppressive". More specifically such soils are also said to be "remediated" although the term currently refers to soils cleansed of unwanted chemical substances. The Pinckard patent, U.S. Pat. No. 4,164,405, p. 5, lines 13-15, states, and we quote . . . "Organic type insecticidal poisons such as toxaphene, DDT, dieldrin or aldrin originally spplied to the growing crop are removed". In that statement Pinckard was referring to the insecticidal residues remaining on the cotton crop waste after it had been separated from the seed and lint by the gin and before the plant material had been composted or otherwise disposed of.
While using multiton quantities of the above described compost for cleansing field crop soils that contained, in addition to plant disease causing agents, 200 ppm of DDT and its isomers, a large pile was left on a garden soil for several weeks before being scattered on the garden. While digging into the soil-compost mix we observed the mix was inhabited by earthworms which are known to be sensitive to the chlorinated aromatic hydrocarbon pesticides. Later tests demonstrated that soils contaminated with several unwanted chemical substances, including soil borne plant pathogens, could be cleansed, or remediated, by mixing with composted (treated) cotton gin waste (or trash) and that the same result could be obtained with composted alfalfa hay but not with cereal straw or common suburban leaf litter. The difference between the raw materials for composting appeared to be their carbon:nitrogen ratios. Those organic raw materials having C:N ratios of approximately 10:1 to 30:1 produced a compost suppressive of soil borne plant pathogens and at the same time, in due course, cleansed the soils of certain unwanted chemical entities. Further research led us to investigate the several well known details of the art of composting in relation to cleansing soils of unwanted entities and to improvements disclosed herein, thus teaching how contaminated soils may be cleansed with composted high nitrogen to carbon ratio plant materials but not with ordinary plant materials or leaf litter such as cereal straw which have C:N ratios approaching 100:1 or more. These facts have not been disclosed heretofore.
Among the first U.S. patent documents reviewed was the Gorby patent, U.S. Pat. No. 2,947,619, issued Aug. 2, 1960 disclosing a process for composting wastes of several kinds by repeated aeration at temperatures of 50.degree. to 70.degree. C. and moisture contents of 40-60%. The Gorby patent while being a disclosure of the prior art bears no relation to our invention for soil remediation.
The Varro, et al., U.S. Pat. No. 3,233,976, issued Feb. 8, 1966, discloses appartus in which organic wastes are converted to fertilizer by aerobic fermentation. It is unrelated to our invention for soil remediation.
The Linn patent, U.S. Pat. No. 3,616,204, issued Oct. 26, 1971, discloses a method for soil restoration (bioremediation) after being contaminated with a petroleum hydrocarbon. The Linn patent discloses, as do several others, inoculating the contaminated soil with cultures of identified microorganisms known to degrade the unwanted contaminants while feeding such organisms appropriate nutrients under controlled laboratory conditions or in the field. The above described approach to soil remediation is likely to be impractical because of soil microbial competition as discussed by Alexander (Alexander, M. 1977. Soil Microbiology, p. 410, "microbial competition", John Wiley & Sons, NY). Many microorganisms compete with each other for nutrients, some protecting themselves by generating antibiotics and while the above hypothesis of soil remediation as delineated by Linn and others may be effective in a sterile substrate it has failed in numerous non sterile substrates as Alexander implies and as my experience has confirmed. For this reason I have turned to the special non sterile substrate as disclosed herein.
The Durrell U.S. Pat. No. 3,762,910, issued Oct. 2, 1973, converts plant nutrients from the passive state to an active state by composting plant material in a trench. It bears no relation to soil remediation as disclosed in our invention.
The Varro patent, U.S. Pat. No. 4,050,917, issued Sept. 27, 1977, discloses a process for composting waste in a heated environment on a series of moving belts and bears no relation to soil remediation.
The Pinckard patents, U.S. Pat. Nos. 4,164,405, issued Aug. 14, 1979, and 4,229,442, issued Oct. 21, 1980, disclosed how cotton crop waste may be cleansed of unwanted identified plant pathogens and chlorinated hydrocarbon insecticides.
The Khoroshavin, et al., patent, U.S. Pat. No. 4,317,670, issued Mar. 2, 1982, remediates industrial waste heaps by leveling, fertilizing, plowing, planting, watering and inoculating with common soil inhabiting fungi; nothing in this invention relates to our claims excepting well known methods of the art.
The Norris, et al., patent, U.S. Pat. No. 4,849,360, issued July 18, 1989, is one of the most recent patents issued for soil remediation. It discloses use of a container for soils contaminated with petroleum hydrocarbons through which air is forced wherein soil remediation depends upon the indigenous microflora after being enriched with phosphorus and nitrogen nutrients.
After reviewing the U.S. patent documents mentioned above and some of the current literature on bioremediation of contaminated soils it is obvious that improvements must include the remediation of unwanted biological entities as well as chemical entities. Another improvement is the identification of specific organic raw materials with suitable carbon:nitrogen ratios for generating the numbers and kinds of oxidative microorganisms necessary for cleansing the soils. A third improvement is the disclosure of the steps necessary for cleansing contaminated soils of unwanted entities.